Li-Ion Capacitors Based on Pre-fluorinated Lithium Powder Prepared with Perfluororesin (CYTOP) as Fluorine Source
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https://doi.org/10.1007/s11664-020-08470-7 Ó 2020 The Minerals, Metals & Materials Society
Li-Ion Capacitors Based on Pre-fluorinated Lithium Powder Prepared with Perfluororesin (CYTOP) as Fluorine Source HU HAO,1 XIAOGANG SUN,1,2 CHEN WEI,1 WEI CHENGCHENG,1 HUANG YAPAN,1 and LIANG GUODONG1 1.—Majoring in Mechantronics Engineering, Nanchang University, Nanchang, China. 2.—e-mail: [email protected]
In order to inhibit the formation of lithium dendrites and solid electrolyte interface films, prevent the corrosion of electrolyte to lithium powder (Li) and improve the electrochemical properties of a lithium ion capacitor (LIC), the lithium powder was fluorinated at high temperature under the protection of nitrogen (N2) by using perfluororesin (CYTOP) as the fluorine source to obtain lithium/lithium fluoride powder (Li@LiF). Li@LiF was pre-embedded in the LIC-cathode sheet and assembled into the LIC. Scanning electron microscopy and x-ray diffraction were used to analyze and test the materials and electrode sheets. The electrochemical properties of the LIC were studied by constantcurrent charge and discharge (GCD) and electrochemical impedance spectroscopy. Experimental results showed that the lithium powder was successfully fluorinated, and that Li@LiF pre-embedded in the cathode can modify the electrochemical properties of the devices that store electrical charge. The specific capacitance of GCD reached 51.92 F g1 at a current density of 50 mA g1. In the range of 50 mA g1 to 700 mA g1, the smallest power density reached 68.51 Wh kg1 and the highest energy density reached 1.02 kW kg1. After 2000 invariant current charge and discharge cycles, the capacitance remained at about 96%. Key words: Lithium powder, fluorination, lithium ion capacitor
INTRODUCTION With the rapid development of the world economy as well as the rapid growth of the population, traditional chemical energy sources are being exhausted and environmental pollution is increasingly serious, motivating vigorous development of green sustainable energy and the storage devices. Among energy storage solutions, lithium ion batteries (LIBs) and supercapacitors (SCs) have drawn much attention due to their excellent performance.1–8 Of these two solutions, each has its own merits and demerits. LIBs have high energy density
(Received January 28, 2020; accepted September 3, 2020)
but poor rate performance, while SCs offer high power density but low energy storage. Researchers have recently proposed a new supercapacitor. The anode adopts the activated carbon (AC) material of the electric double-layer capacitor (EDLC), while the cathode adopts the graphite cathode material of the LIB. By pre-embedding lithium in the graphite cathode, the potential of the cathode is reduced to equivalence with that of lithium. In this way, the voltage of the capacitor can reach 4 V, and its energy density can be several times higher than that of an EDLC. This new capacitor has the same power density as that of an EDLC, and its cyclic life (LIC) can reach more than 100,000 r
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